This invention relates generally to fuel injectors, and more specifically to reverse flow check valves within fuel injectors.
Occasionally, an injector nozzle of a fuel injector will become leaky, and after an injection event, allow hot combustion gases from the engine cylinder to leak past the nozzle outlet and travel upwards into the nozzle supply passage of the fuel injector. If the gases are permitted to continue to travel upwards and reach the fuel pressurization chamber, the fuel injector will inject less than a predicted amount of fuel, and can eventually be unable to pressurize fuel and inject it into the engine cylinder.
Typically, gases have been blocked from the fuel pressurization chamber by reverse flow check valve assemblies having a variety of structures. One example of such a check valve assembly is shown in co-owned U.S. Pat. No. 5,287,838 issued to Wells on Feb. 22, 1994. The function of the check valve assembly is to permit communication of high pressure fuel from the fuel pressurization chamber to the nozzle outlet of the fuel injector during an injection phase, but to prevent communication (i.e., reverse flow) of engine cylinder combustion gas from the nozzle to the fuel pressurization chamber at the end of an injection event and during a non-injection phase if the nozzle of the fuel injector becomes leaky.
Referring to FIG. 1, there is shown a partial sectioned side diagrammatic view of a fuel injector 10 according to the above identified patent. The fuel injector 10 consists of an injector body 11 that includes a barrel 33 separated from a stop component 42 by a relatively thin plate 50. A plunger 13 is movably positioned along a centerline 12 within the injector body 11. The plunger 13, the barrel 33 and the plate 50 define a fuel pressurization chamber 14 that is fluidly connected to a fuel tank (not shown) via a fuel supply line 30. When the plunger 13 is driven downward, it advances along the centerline 12 in order to pressurize fuel delivered from the fuel tank (not shown) via the fuel supply line 30. A check valve 32 is positioned within the fuel supply line 30. The check valve 32 is in its closed position in which it blocks fluid communication between the fuel pressurization chamber 14 and the fuel supply line 30 when the plunger 13 is advancing downward and increasing the pressure within the fuel pressurization chamber 14. When the plunger 13 is returning to its upward position, the pressure within the pressurization chamber 14 decreases such that the check valve 32 opens and low pressure fuel within the fuel supply line 30 can flow past the check valve 32 and into the fuel pressurization chamber 14.
The injector body 11 defines a nozzle supply passage 15, a nozzle outlet 17, and a guide bore 54. A needle valve is positioned in the injector body 11 and has a needle valve member 20 that is movable between a first position, in which the nozzle outlet 17 is open, and a second position, in which the nozzle outlet 17 is closed. The needle valve member 20 has an opening hydraulic surface 21 that is exposed to fluid pressure within the nozzle supply passage 15, but is biased toward a closed position by a compressed spring 22. When the needle valve member 20 is in its open position, a stop surface of the needle valve member 20 is in contact with the stop component 42, and the nozzle outlet 17 is opened to allow pressurized fuel to be injected into the engine cylinder (not shown).
The fuel pressurization chamber 14 is fluidly connected to the nozzle outlet 17 via the nozzle supply passage 15, which includes the guide bore 54. Positioned within the guide bore 54, there is a reverse flow check valve assembly that includes a reverse flow check 52, the plate 50, and the stop component 42. The reverse flow check 52 is preferably a flat circular plate and defines a flow passage 53. The flow passage 53 is preferably cylindrical and centrally positioned within the reverse flow check 52 and is fluidly connected to the nozzle supply passage 15. The plate 50, which is preferably flat, is positioned between the barrel 33 and the stop component 42 and defines a pair of kidney-shaped or crescent-shaped holes 51, which are fluidly connected to the fuel pressurization chamber 14. The flow passage 53 of the reverse flow check 52 is radially inwardly spaced from the kidney holes 51 of the plate 50 and is arranged so that the nozzle supply passage 15 is blocked from the pressurization chamber 14 when the reverse flow check 52 and the plate 50 are in contact. The reverse flow check 52 is movable between an open position and closed position. When in its open position, as shown, the reverse flow check 52 is in contact with the stop component 42, and the fuel pressurization chamber 14 is fluidly connected to the nozzle supply passage 15 via the kidney holes 51 of the plate 50 and the flow passage 53 of the reverse flow check 52.
Prior to an injection event, the plunger 13 is driven downward by a hydraulic intensifier piston or a tappet along a centerline 12 of the fuel injector 10 toward its downward position. This greatly increases the pressure within the upper portion of the nozzle supply passage 15 which includes the fuel pressurization chamber 14 and the lower portion of the nozzle supply passage 15. The increased pressure within the fuel pressurization chamber 14 will also close the check valve 32, blocking fluid communication between the fuel pressurization chamber 14 and the fuel tank (not shown) via the fuel supply line 30. The reverse flow check 52 will be in its first, or open, position, and in contact with the stop component 42. Thus, the pressurized fuel will flow from the fuel pressurization chamber 14 through kidney holes 51 within the plate 50 and through the flow passage 53 of the reverse flow check 52 to the lower portion of the nozzle supply passage 15. Thus, during an injection event, the fuel pressurization chamber 14 is fluid connected to the lower portion of the nozzle supply passage 15.
Shortly before the desired amount of pressurized fuel is injected into the engine cylinder via the nozzle outlet 17 of the fuel injector 10, the plunger 13 will stop moving downward, resulting in a fuel pressure drop to below valve closing pressure. This causes the needle valve member 20 to move to its closed position under the action of spring 22. Towards the end of the movement of the needle valve member 20 to its closed position, there is a reverse flow of pressurized fuel within the lower portion of the nozzle supply passage 15. The reverse flow of fuel will lift the reverse flow check 52 out of contact with the stop component 42. The reverse flow check 52 will be lifted upward until it is in contact with the plate 50 and, thus, in its second, or closed, position. Due to the positioning and placement of the kidney holes 51 of the plate 50 and the flow passage 53 of the reverse flow check 52, fluid communication between the fuel pressurization chamber 14 and the nozzle supply passage 15 will be blocked. Gas ingestion can occur over a brief instant as the needle valve member 20 is not yet closed while fuel pressure has dropped below cylinder pressure. If any engine cylinder combustion gases enter through the nozzle outlet 17 into the lower portion of the nozzle supply passage 15, they will be blocked from fluid communication with the fuel pressurization chamber 14 when the reverse flow check 52 is in its closed position. Thus, the prior injector prevents gas from being trapped within the fuel pressurization chamber 14 by utilizing the reverse flow check 52, the plate 51, and the stop component 42.
The hydraulic pressure acting on the plunger 13 is then reduced allowing the plunger 13 to retract along the centerline 12 to its upward position under the action of its biasing spring 16. As the plunger 13 retracts, the pressure within the fuel pressurization chamber 14 preferably will lessen such that fuel from the fuel tank (not shown) can be drawn into the fuel pressurization chamber 14 via the fuel supply line 30 past the check valve 32. The injection process can once again begin.
Although these reverse flow check valve assemblies have performed well, there is room for improvement. For instance, the reverse flow check valve assemblies limit combustion gases from leaking into the fuel pressurization chamber 14 through the nozzle outlet 17 by blocking fluid communication between the lower portion of the nozzle supply passage 15 and the fuel pressurization chamber 14 toward the end of an injection event. However, the reverse check valve assemblies do not prevent all gases ingested through the nozzle outlet 17 from traveling to the fuel pressurization chamber 14. Because the reverse flow check 52 remains in the closed position only for a limited time when the reverse flow of fuel is hydraulically displacing it, there is the possibility that combustion gases can leak past the nozzle outlet 17 after the hydraulic pressure caused by the reverse flow of fuel within the nozzle supply passage has subsided. This can occur due to excessive wear on the needle valve seat. Further, the reverse control valve assembly cannot prevent gases from leaking into the fuel pressurization chambers 14 by other means than gas ingestion through the nozzle outlet 17. Theoretically, gas trapping may occur if t hot combustion gases leak past seals on the outer surface of the fuel injector 10 and travel upward along the outer surface of the fuel injector 10 until they reach the area in the engine head where the fuel supply line 30 exists. The gases then mix with the low pressure fuel and are delivered to the fuel pressurization chamber 14.
Occasionally, hot combustion gases are ingested through the injector tip and/or enter via the fuel supply are trapped within the fuel pressurization chamber 14 and the nozzle supply passage 15 by the check valve 32 and the direct needle control valve member 20. The trapped gas creates pressure within the fuel pressurization chamber 14 sufficient to prohibit the check valve 32 from rising off its seat and allowing low pressure fuel into the fuel pressurization chamber 14. Thus, the fuel pressurization chamber 14 is blocked from fluid communication with the fuel supply line 30 by the check valve 32. The pressure caused by the trapped gas acting on the opening hydraulic surface 21 within the nozzle supply passage 15 is sometimes not great enough to overcome the biasing spring 22 of the needle valve member 20. Thus, the nozzle supply passage 15, is blocked from fluid communication with the nozzle outlet 17. When this gas trapping occurs, the plunger 13 will advance downward to pressurize the fuel, but there will be little or no fuel within the fuel pressurization chamber 14 because the fuel pressurization chamber 14 is blocked from the fuel supply line 30 by the closed check valve 32. The gas can never reach a high enough pressure to open the needle valve member 20 and the gas pressure never drops low enough to allow the check valve 32 to lift to its open position to allow fuel into the fuel pressurization chamber 14. Thus, the plunger 13 reciprocates up and down but nothing happens with the fuel injector 10. In these cases, the fuel injector 10 needs a means for re-priming itself.
Also, during assembly of new fuel injectors 10, gases, other than engine cylinder gases, can be trapped within the empty space within the fuel pressurization chambers 14. If the gas trapping occurs in a new fuel injector 10, the fuel injector 10 is unable to prime itself and inject fuel into the engine cylinder. If the gas trapping occurs during operation of a fuel injector 10, the fuel injector 10 is unable to re-prime itself by pushing the gases out of the nozzle outlet 17. In either situation, once gases are in the fuel pressurization chamber 14, the pressure within the nozzle supply passage 15 will be insufficient to open the nozzle outlet 17 and the pressure within the fuel pressurization chamber 14 will be too great for the check valve 32 to open. Thus, because the fuel injector 10 has no way of pushing the gas pressure out of the fuel pressurization chamber 14, the plunger 13 will reciprocate up and down and nothing will happen within the fuel injector 10.
Moreover, the plate 50 used as a stop for the reverse flow check 52 is subject to fretting, and the thin plate decreases the available height of the stop component 42 which in return increases the risk of oil to fuel transfer.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the invention, a fuel injector comprises an injector body that defines a nozzle supply passage and a nozzle outlet. Within the injector body is positioned a reverse flow valve member that has an opening hydraulic surface exposed to fluid pressure in an upper portion of the nozzle supply passage. The reverse flow valve member is moveable between a closed position in which the nozzle supply passage is blocked and an open position in which the nozzle supply passage is open. The reverse flow valve member is biased toward the closed positioned by a compressed spring.
In another aspect, a fuel injector includes an injector body defining a nozzle outlet. The injector body also includes a barrel that is in contact with a stop component. A movable plunger is at least partially positioned in the barrel. A reverse flow valve member is trapped between the barrel and the stop component, and is movable between a first position and a second position. The plunger, the reverse flow valve member, and the injector body define a nozzle supply passage that includes a fuel pressurization chamber. When the reverse flow valve member is in the second position, the nozzle supply passage is fluidly connected to a lower portion of the nozzle supply passage. A compressed spring is operably positioned in the injector body to bias the reverse flow valve member toward the first position, in which the fuel pressurization chamber is blocked from the lower portion of the nozzle supply passage.
In still another aspect, gas ingestion in a fuel injector is reduced by moving a reverse flow valve member at least in part with a spring to a position that blocks a downstream portion of a nozzle supply passage to an upstream portion of the nozzle supply passage.